Rotary internal combustion engine with pilot subchamber

ABSTRACT

A rotary engine having an insert in a peripheral wall of the stator body, the insert being made of a material having a greater heat resistance than that of the peripheral wall, having a subchamber defined therein and having an inner surface, the subchamber communicating with the cavity through at least one opening defined in the inner surface and having a shape forming a reduced cross-section adjacent the opening, a pilot fuel injector having a tip received in the subchamber, an ignition element having a tip received in the subchamber, and a main fuel injector extending through the stator body and having a tip communicating with the cavity at a location spaced apart from the insert. The subchamber has a volume corresponding to from 5% to 25% of a sum of the minimum volume and the volume of the subchamber. A method of injecting heavy fuel into a Wankel engine is also discussed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/273,534 filed Oct. 14, 2011, which claims priority on provisionalU.S. application No. 61/512,593 filed Jul. 28, 2011, the entire contentsof both of which are incorporated by reference herein.

TECHNICAL FIELD

The application relates generally to a compound engine system includinga rotary internal combustion engine, more particularly, to such a systememploying heavy fuels.

BACKGROUND OF THE ART

Rotary engines, such as for example Wankel engines, use the eccentricrotation of a piston to convert pressure into a rotating motion, insteadof using reciprocating pistons. In these engines, the rotor includes anumber of apex or seal portions which remain in contact with aperipheral wall of the rotor cavity of the engine throughout therotational motion of the rotor to create a plurality of rotatingchambers when the rotor rotates.

Wankel engines are typically used with gasoline or similar fuel, with asingle fuel injector or with two spaced apart fuel injectors. The fuelinjector(s) may be located in a recess adjacent the combustion chamberand defined integrally through the engine housing, to communicate withan ignition member such as for example a spark plug. However, knownarrangements are not optimized for use in a compound cycle engine systemand/or for use with so-called heavy fuels, such as kerosene, and thusroom for improvement exists.

SUMMARY

In one aspect, there is provided a rotary engine comprising a statorbody having an internal cavity defined by two axially spaced apart endwalls and a peripheral wall extending between the end walls, the cavityhaving an epitrochoid shape defining two lobes, a rotor body havingthree circumferentially spaced apex portions, the rotor body beingengaged to an eccentric portion of a shaft to rotate and perform orbitalrevolutions within the cavity with each of the apex portions remainingin sealing engagement with the peripheral wall and separating threerotating chambers of variable volume defined in the cavity around therotor body, an insert in the peripheral wall of the stator body, theinsert being made of a material having a greater heat resistance thanthat of the peripheral wall, the insert having a subchamber definedtherein and having an inner surface bordering the cavity, the subchambercommunicating with the cavity through at least one opening defined inthe inner surface and having a shape forming a reduced cross-sectionadjacent the opening, a pilot fuel injector having a tip received in thesubchamber, an ignition element having a tip received in the subchamber,and a main fuel injector extending through the stator body and having atip communicating with the cavity at a location spaced apart from theinsert.

In another aspect, there is provided a stator body for a Wankel enginecomprising two axially spaced apart end walls, a peripheral wallextending between the end walls and defining an internal cavitytherewith, the cavity having an epitrochoid shape defining two lobes, aninsert in the peripheral wall of the stator body, the insert being madeof a material having a greater heat resistance than that of theperipheral wall, the insert having a subchamber defined therein andhaving an inner surface bordering the cavity, the subchambercommunicating with the cavity through at least one opening defined inthe inner surface and having a shape forming a reduced cross-sectionadjacent the opening, at least one of the insert and the peripheral wallhaving a pilot fuel injector elongated hole defined therethroughcommunicating with the subchamber and sized to receive a pilot fuelinjector therein, at least one of the insert and the peripheral wallhaving an ignition element elongated hole defined therethroughcommunicating with the subchamber and sized to receive an ignitionelement therein, and the peripheral wall having a main fuel injectorelongated hole defined therethrough spaced apart from the insert andsized to receive a main fuel injector therein.

In yet another aspect, there is provided a method of injecting heavyfuel into a Wankel engine having rotating chambers each having a volumevarying between a minimum volume and a maximum volume, the methodcomprising injecting a minor portion of the heavy fuel into a subchamberdefined adjacent to and in sequential communication with each of therotating chambers and having a subchamber volume corresponding to from5% to 25% of a sum of the minimum volume and the subchamber volume,igniting the heavy fuel within the subchamber, partially restricting aflow of the ignited heavy fuel from the subchamber to the rotatingchambers, and injecting a remainder of the heavy fuel into each of therotating chambers sequentially, independently of and spaced apart fromthe subchamber.

In another aspect, there is provided a rotary engine comprising: a rotorbody mounted for eccentric revolutions within a stator body to providerotating chambers of variable volume in an internal cavity of the statorbody, the volume of each chamber varying between a minimum volume and amaximum volume; an insert in a peripheral wall of the stator body, theinsert being made of a material having a greater heat resistance thanthat of the peripheral wall, the insert having a subchamber definedtherein and having an inner surface, the subchamber communicating withthe cavity through at least one opening defined in the inner surface andhaving a shape forming a reduced cross-section adjacent the opening, thesubchamber having a volume corresponding to from 5% to 25% of a sum ofthe minimum volume and the volume of the subchamber; a pilot fuelinjector having a tip received in the subchamber, the tip of the pilotfuel injector extending through an injector opening defined through theinsert; an ignition element received within an ignition element holedefined through the insert, the ignition element having a tip receivedin the subchamber; and a main fuel injector extending through the statorbody and having a tip communicating with the cavity at a location spacedapart from the insert.

In another aspect, there is provided a method of injecting heavy fuelinto a Wankel engine having rotating chambers each having a volumevarying between a minimum volume and a maximum volume, the methodcomprising: injecting a minor portion of the heavy fuel into asubchamber defined adjacent to and in sequential communication with eachof the rotating chambers, the subchamber having a subchamber volumecorresponding to from 5% to 25% of a sum of the minimum volume and thesubchamber volume; igniting the heavy fuel within the subchamber;creating a hot wall around the subchamber by providing the subchamber inan insert received in a wall of a stator of the engine, the insert beingmade of a material more resistant to high temperature than that of thewall; partially restricting a flow of the ignited heavy fuel from thesubchamber to the rotating chambers; and injecting a remainder of theheavy fuel into each of the rotating chambers sequentially,independently of and spaced apart from the subchamber.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1 is a partial, schematic cross-sectional view of a rotary internalcombustion engine in accordance with a particular embodiment;

FIG. 2 is a schematic cross-sectional view of an insert of the engine ofFIG. 1;

FIG. 3 is a schematic cross-sectional view of an insert in accordancewith another embodiment; and

FIG. 4 is a schematic cross-sectional view of an insert in accordancewith a further embodiment.

DETAILED DESCRIPTION

Referring to FIG. 1, a rotary internal combustion engine 10 known as aWankel engine is schematically and partially shown. In a particularembodiment, the rotary engine 10 is used in a compound cycle enginesystem such as described in Lents et al.'s U.S. Pat. No. 7,753,036issued Jul. 13, 2010 or as described in Julien et al.'s U.S. Pat. No.7,775,044 issued Aug. 17, 2010, the entire contents of both of which areincorporated by reference herein. The compound cycle engine system maybe used as a prime mover engine, such as on an aircraft or othervehicle, or in any other suitable application. In any event, in such asystem, air is compressed by a compressor before entering the Wankelengine, and the engine drives one or more turbine(s) of the compoundengine. In another embodiment, the rotary engine 10 is used without aturbocharger, with air at atmospheric pressure.

The engine 10 comprises an outer body 12 having axially-spaced end walls14 with a peripheral wall 18 extending therebetween to form a rotorcavity 20. The inner surface 19 of the peripheral wall 18 of the cavity20 has a profile defining two lobes, which is preferably an epitrochoid.

An inner body or rotor 24 is received within the cavity 20, with thegeometrical axis of the rotor 24 being offset from and parallel to theaxis of the outer body 12. The rotor 24 has axially spaced end faces 26adjacent to the outer body end walls 14, and a peripheral face 28extending therebetween. The peripheral face 28 defines threecircumferentially-spaced apex portions 30 (only one of which is shown),and a generally triangular profile with outwardly arched sides. The apexportions 30 are in sealing engagement with the inner surface ofperipheral wall 18 to form three rotating working chambers 32 (only twoof which are partially shown) between the inner rotor 24 and outer body12. A recess 38 is defined in the peripheral face 28 of the rotor 24between each pair of adjacent apex portions 30, to form part of thecorresponding chamber 32.

The working chambers 32 are sealed. Each rotor apex portion 30 has anapex seal 52 extending from one end face 26 to the other and protrudingradially from the peripheral face 28. Each apex seal 52 is biasedradially outwardly against the peripheral wall 18 through a respectivespring. An end seal 54 engages each end of each apex seal 52, and isbiased against the respective end wall 14 through a suitable spring.Each end face 26 of the rotor 24 has at least one arc-shaped face seal60 running from each apex portion 30 to each adjacent apex portion 30,adjacent to but inwardly of the rotor periphery throughout its length. Aspring urges each face seal 60 axially outwardly so that the face seal60 projects axially away from the adjacent rotor end face 26 intosealing engagement with the adjacent end wall 14 of the cavity. Eachface seal 60 is in sealing engagement with the end seal 54 adjacent eachend thereof.

Although not shown in the Figures, the rotor 24 is journaled on aneccentric portion of a shaft and includes a phasing gear co-axial withthe rotor axis, which is meshed with a fixed stator phasing gear securedto the outer body co-axially with the shaft. The shaft rotates the rotor24 and the meshed gears guide the rotor 24 to perform orbitalrevolutions within the rotor cavity. The shaft rotates three times foreach complete rotation of the rotor 24 as it moves around the rotorcavity 20. Oil seals are provided around the phasing gear to preventleakage flow of lubricating oil radially outwardly thereof between therespective rotor end face 26 and outer body end wall 14.

At least one inlet port (not shown) is defined through one of the endwalls 14 or the peripheral wall 18 for admitting air (atmospheric orcompressed) into one of the working chambers 32, and at least oneexhaust port (not shown) is defined through one of the end walls 14 orthe peripheral wall 18 for discharge of the exhaust gases from theworking chambers 32. The inlet and exhaust ports are positioned relativeto each other and relative to the ignition member and fuel injectors(further described below) such that during each rotation of the rotor24, each chamber 32 moves around the cavity 20 with a variable volume toundergo the four phases of intake, compression, expansion and exhaust,these phases being similar to the strokes in a reciprocating-typeinternal combustion engine having a four-stroke cycle.

In a particular embodiment, these ports are arranged such that therotary engine 10 operates under the principle of the Miller or Atkinsoncycle, with its volumetric compression ratio lower than its volumetricexpansion ratio. In another embodiment, the ports are arranged such thatthe volumetric compression and expansion ratios are equal or similar toone another.

An insert 34 is received in a corresponding hole 36 defined through theperipheral wall 18 of the outer body 12, for pilot fuel injection andignition. The peripheral wall 18 also has a main injector elongated hole40 defined therethrough, in communication with the rotor cavity 20 andspaced apart from the insert 34. A main fuel injector 42 is received andretained within this corresponding hole 40, with the tip 44 of the maininjector 42 communicating with the cavity 20 at a point spaced apartfrom the insert 34. The main injector 42 is located rearwardly of theinsert 34 with respect to the direction R of the rotor rotation andrevolution, and is angled to direct fuel forwardly into each of therotating chambers 32 sequentially with a tip hole pattern designed foran adequate spray.

Referring particularly to FIG. 2, the insert includes an elongated body46 extending across a thickness of the peripheral wall 18, with anenlarged flange 48 at its outer end which is biased away from a shoulder50 defined in the peripheral wall 18, and against a gasket (not shown)made of an appropriate type of heat resistant material such as a silicabased material. A washer 56, such as for example a steel or titaniumwasher, and spring 58, such as for example a wave spring or a Bellevillespring, are provided between the flange 48 and the shoulder 50 of theperipheral wall 18. The spring 58 biases the body 46 against a cover 62having a cross-section greater than that of the hole 36 and extendingover an outer surface 64 of the peripheral wall 18. The cover 62 isconnected to the peripheral wall 18, for example through brazing.Alternate types of connections can also be used, including but notlimited to a connection through fasteners such as bolts, to helpfacilitate replacement of the insert if necessary.

The insert body 46 has an inner surface 66 which is continuous with theinner surface 19 of the peripheral wall 20 to define the cavity 20. Theinsert hole 36 in the wall 18 defines a flange 68 extending in theinsert hole 36 adjacent the inner surface 19, and the inner end of theinsert body 46 is complementarily shaped to engage this flange 68, witha gasket 70 being received therebetween.

The insert body 46 is made of a material having a greater heatresistance than that of the peripheral wall 18, which in a particularembodiment is made of aluminium. In this particular embodiment, theinsert body 46 is made of an appropriate type of ceramic.

The insert body 46 has a pilot subchamber 72 defined therein incommunication with the rotor cavity 20. In the embodiment shown, thesubchamber 72 has a circular cross-section; alternate shapes are alsopossible. The subchamber 72 communicates with the cavity through atleast one opening 74 defined in the inner surface 66. The subchamber 72has a shape forming a reduced cross-section adjacent the opening 74,such that the opening 74 defines a restriction to the flow between thesubchamber 72 and the cavity 20. The opening 74 may have various shapesand/or be defined by a pattern of multiple holes.

The peripheral wall 18 has a pilot injector elongated hole 76 definedtherethrough in proximity of the insert 34, extending at a non-zeroangle with respect to a surface of an outer wall of the insert 34, andin communication with the subchamber 72. A pilot fuel injector 78 isreceived and retained within the corresponding hole 76, with the tip 80of the pilot injector 78 being received in the subchamber 72. As can beseen in FIG. 2, the insert body 46 has an injector opening definedtherethrough providing the communication between the pilot injectorelongated hole 76 and the subchamber 72, and the tip 80 of the pilotinjector 78 is received in the subchamber 72 through this injectoropening, with a major part of the pilot injector 78 being received inthe pilot injector elongated hole 76 outside of the insert 34.

The insert body 46 and cover 62 have an ignition element elongated hole82 defined therein extending along the direction of the transverse axisT of the outer body 12, also in communication with the subchamber 72. Anignition element 84 is received and retained within the correspondinghole 82, with the tip 86 of the ignition element 84 being received inthe subchamber 72. In the embodiment shown, the ignition element 84 is aglow plug. Alternate types of ignition elements 84 which may be usedinclude, but are not limited to, plasma ignition, laser ignition, sparkplug, microwave, etc.

The pilot injector 78 and main injector 42 inject heavy fuel, e.g.diesel, kerosene (jet fuel), equivalent biofuel, etc. into the chambers32. In a particular embodiment, at least 0.5% and up to 20% of the fuelis injected through the pilot injector 78, and the remainder is injectedthrough the main injector 42. In another particular embodiment, at most10% of the fuel is injected through the pilot injector 78. In anotherparticular embodiment, at most 5% of the fuel is injected through thepilot injector 78. The main injector 42 injects the fuel such that eachrotating chamber 32 when in the combustion phase contains a lean mixtureof air and fuel.

Referring to FIG. 3, an insert 134 according to another embodiment isshown, engaged to the same outer body 12. The insert 134 extends acrossa thickness of the peripheral wall 18, and includes an inner bodyportion 146 and an outer body portion 162 which are attached together,for example through a high temperature braze joint 188. The outer bodyportion 162 has an enlarged flange 148 at its outer end which abuts theouter surface 64 of the peripheral wall 18 and is connected thereto, forexample through bolts with appropriate sealing such as a gasket or crushseal (not shown). Alternate types of connections can also be used,including but not limited to a brazed connection.

The inner body portion 146 has an inner surface 166 which is continuouswith the inner surface 19 of the peripheral wall 18 to define the cavity20. The inner end of the inner body portion 146 is complementarilyshaped to engage the flange 68 extending in the insert hole 36 adjacentthe inner surface 19, with a gasket 70 being received therebetween.

In this particular embodiment, the body portions 146, 162 are made of anappropriate type of super alloy such as a Nickel based super alloy.

The pilot subchamber 72 is defined in the insert 134 at the junctionbetween the body portions 146, 162, with the inner body portion 146defining the opening 74 for communication between the subchamber 72 andthe cavity 20. The outer body portion 162 has the ignition elementelongated hole 82 defined therein along the direction of the transverseaxis T and in communication with the subchamber 72. The ignition element84 is received and retained within the corresponding hole 82, forexample through threaded engagement. As in the previous embodiment, thetip 86 of the ignition element 84 is received in the subchamber 72.

Referring to FIG. 4, an insert 234 according to another embodiment isshown. The insert 234 is received in a corresponding hole 236 definedthrough the peripheral wall 18. The insert 234 includes an inner bodyportion 246 and an outer body portion 262 which are attached together,for example through a high temperature braze joint, with the subchamber72 being defined at the junction of the two portions 246, 262. The innerbody portion 246 defines the opening 74 for communication between thesubchamber 72 and the cavity 20.

The outer body portion 262 has the ignition element elongated hole 82defined therethrough in communication with the subchamber 72. The outerbody portion 262 includes an inner enlarged section 245 connected to theinner body portion 246 and defining the subchamber 72. The enlargedsection 245 extends substantially across the width of the hole 236around the subchamber 72, then tapers to a reduced width section 247extending therefrom. The reduced width section 247 has at its outer endan enlarged flange 248 which abuts a shoulder 250 defined in the outersurface 64 of the peripheral wall 18 around the hole 236. An outersection 249, which in the embodiment shown has a width intermediate thatof the sections 245 and 247, extends outwardly from the flange 248. Theflange is connected to the shoulder, for example through bolts (notshown) with appropriate sealing such as a crush seal or a gasket (notshown) made of high temperature material, for example a silica basedmaterial or grafoil, between the flange 248 and shoulder 250. Alternatetypes of connections can also be used.

The inner body portion 246 has an inner surface 266 which is continuouswith the inner surface 19 of the peripheral wall 18 to define the cavity20. The inner body portion 246 includes a groove defined therearoundnear the inner surface 266, in which an appropriate seal 251, forexample a silica based gasket tape, is received in contact with thewalls of the insert hole 236. In this embodiment, the walls of theinsert holes 236 are straight adjacent the inner surface 19, i.e. thereis no flange adjacent the inner surface 19.

The volume of the subchamber 72 in the insert 34, 134, 234 is selectedto obtain a stoichiometric mixture around ignition within an acceptabledelay, with some of the exhaust product from the previous combustioncycle remaining in the subchamber 72. In a particular embodiment, thevolume of the subchamber 72 is at least 0.5% and up to 3.5% of thedisplacement volume, with the displacement volume being defined as thedifference between the maximum and minimum volumes of one chamber 32. Inanother particular embodiment, the volume of the subchamber 72corresponds to from about 0.625% to about 1.25% of the displacementvolume.

The volume of the subchamber 72 may also be defined as a portion of thecombustion volume, which is the sum of the minimum chamber volume Vmin(including the recess 38) and the volume of the subchamber V2 itself. Ina particular embodiment the subchamber 72 has a volume corresponding tofrom 5% to 25% of the combustion volume, i.e. V2=5% to 25% of (V2+Vmin).In another particular embodiment, the subchamber 72 has a volumecorresponding to from 10% to 12% of the combustion volume, i.e. V2=10%to 12% of (V2+Vmin).

The subchamber 72 may help create a stable and powerful ignition zone toignite the overall lean main combustion chamber 32 to create thestratified charge combustion. The subchamber 72 may improve combustionstability, particularly but not exclusively for a rotary engine whichoperates with heavy fuel below the self ignition of fuel. The insert 34,134, 234 made of a heat resistant material may advantageously create ahot wall around the subchamber which may further help with ignitionstability.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the invention(s)disclosed. For example, the mechanical arrangement of the Wankel enginedescribed above is merely one example of many possible configurationswhich are suitable for use with the present invention(s). Any suitableinjector configuration and arrangement may be used. Hence, modificationswhich fall within the scope of the present invention will be apparent tothose skilled in the art, in light of a review of this disclosure, andsuch modifications are intended to fall within the appended claims.

The invention claimed is:
 1. A rotary engine comprising: a rotor bodymounted for eccentric revolutions within a stator body to providerotating chambers of variable volume in an internal cavity of the statorbody, the volume of each chamber varying between a minimum volume and amaximum volume; an insert in a peripheral wall of the stator body, theinsert being made of a material having a greater heat resistance thanthat of the peripheral wall, the insert having a subchamber definedtherein and having an inner surface, the subchamber communicating withthe cavity through at least one opening defined in the inner surface andhaving a shape forming a reduced cross-section adjacent the opening, thesubchamber having a volume corresponding to from 5% to 25% of a sum ofthe minimum volume and the volume of the subchamber; a pilot fuelinjector having a tip received in the subchamber, the tip of the pilotfuel injector extending through an injector opening defined through theinsert; an ignition element received within an ignition element holedefined through the insert, the ignition element having a tip receivedin the subchamber; and a main fuel injector extending through the statorbody and having a tip communicating with the cavity at a location spacedapart from the insert.
 2. The engine as defined in claim 1, wherein adifference between the maximum volume and the minimum volume defines adisplacement volume, the subchamber having a volume of at least 0.5% ofthe displacement volume and at most 3.5% of the displacement volume. 3.The engine as defined in claim 1, wherein a difference between themaximum volume and the minimum volume defines a displacement volume, thesubchamber having a volume of at least 0.625% of the displacementvolume.
 4. The engine as defined in claim 1, wherein a differencebetween the maximum volume and the minimum volume defines a displacementvolume, the subchamber having a volume of 1.25% the displacement volume.5. The engine as defined in claim 1, wherein the volume of thesubchamber corresponds to from 10% to 12% of the sum of the minimumvolume and the volume of the subchamber.
 6. The engine as defined inclaim 1, wherein the insert is made of ceramic or super alloy.
 7. Theengine as defined in claim 1, wherein the pilot injector extends throughthe peripheral wall at a non-zero angle with respect to a surface of anouter wall of the insert with only a portion thereof extending withinthe insert.
 8. The engine as defined in claim 1, wherein the pilotinjector extends through the peripheral wall at a non-zero angle withrespect to a longitudinal direction of the insert.
 9. The engine asdefined in claim 1, further comprising a heavy fuel source incommunication with the fuel injectors.
 10. A method of injecting heavyfuel into a Wankel engine having rotating chambers each having a volumevarying between a minimum volume and a maximum volume, the methodcomprising: injecting a minor portion of the heavy fuel into asubchamber defined adjacent to and in sequential communication with eachof the rotating chambers, the subchamber having a subchamber volumecorresponding to from 5% to 25% of a sum of the minimum volume and thesubchamber volume; igniting the heavy fuel within the subchamber;creating a hot wall around the subchamber by providing the subchamber inan insert received in a wall of a stator of the engine, the insert beingmade of a material more resistant to high temperature than that of thewall; partially restricting a flow of the ignited heavy fuel from thesubchamber to the rotating chambers; and injecting a remainder of theheavy fuel into each of the rotating chambers sequentially,independently of and spaced apart from the subchamber.
 11. The method asdefined in claim 10, wherein injecting a minor portion of the heavy fuelinto the subchamber includes injecting from 0.5% to 20% of the heavyfuel.
 12. The method as defined in claim 10, wherein injecting a minorportion of the heavy fuel into the subchamber includes injecting from 5%to 10% of the heavy fuel.
 13. The method as defined in claim 10, whereininjecting the minor portion of the heavy fuel is done into thesubchamber with the subchamber volume corresponding to from 10% to 12%of the sum of the minimum volume and the subchamber volume.
 14. Themethod as defined in claim 10, wherein the insert is received in aperipheral wall of the engine.
 15. The method as defined in claim 10,wherein injecting the minor portion of the heavy fuel is done in anangled direction with respect to a central transverse axis of a statorof the engine.
 16. The method as defined in claim 10, wherein the insertis made of ceramic or super alloy.